The invention has as an object to provide a device for detecting water inflow inside a seismic streamer.
More particularly, the invention concerns a device for detecting parasitic electric connections occurring between conductor wires contained in the different sections of a seismic streamer, as a result of a water penetration therein, due to a sealing defect.
The prior art marine seismic prospecting methods generally comprise the transmission of acoustic waves through water, the reception of the echoes of said seismic waves after reflections on different layers or mirrors of submerged formations and their recording. The reception of echoes is effected by means of receivers in a seismic streamer of great length formed of a plurality of interconnected streamer sections. Each streamer section comprises a tight tubular sheath provided at each end with a connecting device. Each streamer section or some of them comprise a plurality of seismic wave receivers (hydrophones), or groups of electrically interconnected receivers, arranged at regular intervals inside the sheath. Conducting wires connect the hydrophones or hydrophone groups to electric connectors arranged in each connecting device. The different hydrophone groups of the seismic streamer may either be directly connected to a recording system placed on a towing ship or, in the more recent prior art seismic streamers, to local data acquisition devices formed of electronic assemblies adapted to collect the signals received at a certain number of seismic signal receivers and to transmit them sequentially to the recording system. These local acquisition devices are included in the seismic streamer sections containing the seismic receivers, or in particular sections intercalated between the sections containing the seismic receivers. An acquisition device of this type is described for example in the French published patent application No. 2,471,088.
The different streamer section are filled with an electrically insulating liquid. If, for any reason, the sealing of the sheath is not perfectly achieved, water penetrating inside may establish parasitic electric connections between the conductors transmitting the seismic signals. Moreover, when the seismic streamer comprises a plurality of local seismic data acquisition devices fed with current from the ship through supply lines, the water may establish electric connections between these lines and the conductors used for the transmission of seismic data, which may have as effect to damage the electronic apparatus forming the data acquisition devices.
A known process for detecting a possible water inflow inside a seismic streamer section consists of placing inside the section two parallel electric conductors whose insulating sheath is provided with holes at regular intervals and of connecting these conductors to a current source. The water having penetrated inside the streamer section creates shunts between the holes of the insulating sheath, thereby varying the electric voltage between the two conductors. The variations of this electric voltage, if any, are transmitted permanently or intermittently to a monitoring device placed on the towing ship.